STATISTICAL-METHODS IN INTERPHASE CYTOGENETICS - AN EXPERIMENTAL APPROACH

In situ hybridization (ISH) techniques on interphase cells, or interph ase cytogenetics, have powerful potential clinical and biological appl ications, such as detection of minimal residual disease, early relapse , and the study of clonal evolution and expansion in neoplasia. Much a ttention has been paid to issues related to ISH data acquisition, i.e. , the numbers, colors, intensities, and spatial relationships of hybri dization signals. The methodology concerning data analysis, which is o f prime importance for clinical applications, however, is less well in vestigated. We have studied the latter for the detection of small mono somic and trisomic cell populations using various mixtures of human fe male and male cells. With a chromosome X specific probe, the male cell s simulated monosomic subpopulations of 0, 1, 5, 10, 50, 90, 95, 99, a nd 100%. Analogously, when a (7 + Y) specific probe combination was us ed, containing a mixture of chromosome No. 7 and Y-specific DNA, the m ale cells simulated trisomic cell populations. Probes specific for chr omosomes Nos. 1, 7,8, and 9 were used for estimation of ISH artifacts. Three statistical tests, the Kolmogorov-Smirnov test, the multiple-pr oportion test, and the z'-max test, were applied to the empirical data using the control data as a reference for ISH artifacts. The Kolmogor ov-Smirnov test was found to be inferior for discrimination of small m onosomic or trisomic cell populations. The other two tests showed that when 400 cells were evaluated, and using selected control probes, mon osomy X could be detected at a frequency of 5% aberrant cells, and tri somy 7 + Y at a frequency of 1%. A simple-proportion test was develope d for illustration of the quantitative constraints of interphase cytog enetics. For detection of 1% aberrant cells and given an ISH artifact rate of 10%, 10,173 cells must be evaluated. These results indicate th at automated ISH evaluation is imperative for clinical and biological applications. (C) 1993 Wiley-Liss, Inc.